05-12-2012, 04:09 PM
Variable Valve Timing
Variable Valve Timing.doc (Size: 459.5 KB / Downloads: 23)
INTRODUCTION
Engine breathing is analogous to the breathing of any living organism. At rest, the lungs take in the necessary amount of air for normal function. When running, the lungs and heart work faster to supply more oxygen to the system. Engines can't do that because their breathing apparatus (comprised intake manifolds, intake runners, valves, valve lift and throttle bores) is fixed.
There was a time when engines had to be big to be powerful. There was a time when engines could either be tuned for low-rpm torque or high-rpm power, but not both. There was a time was a time when a specific output of 100 hp per liter was the stuff of racecar fantasies. Today these limitations are all but gone. Getting 100 hp for each liter of displacement is now possible on cars that have to get good gas mileage, emit clean air, act civilized enough for your grandmother to drive them and sell for under $20,000
DEVELOPMENT OF VVT TECHNOLOGY
Honda broke the ice when the NSX debuted in 1991 as the first production car with a variable valve timing system. Honda's VTEC (which sort of stands for Variable valve Timing and lift Electronic Control) system, which has basically remained unchanged since then, is still one of the most effective systems for making ultra high specific output. Ferrari has a really neat way of doing this. The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive. The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. The shaft still spins just like a regular camshaft, but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized.
Porsche’s VARIOCAM
Porsche's VarioCam, used first on the 968 and know used without the fanfare on all (both) of their engines is as simple as it gets. With VarioCam, the crank drives the exhaust cam, and the intake cam is driven, via a short chain, by the exhaust cam. In order to advance and retard the intake cam, the chain tensioner on that short chain simply shifts up and down, moving the extra length in the chain from the tight side to the slack side. When the tight side has no extra chain (i.e. the chain is straight), the intake cam is fully advanced, as more chain is shifted to the tight side, the cam is retarded.
Ferrari’ Cam Advance Mechanism
Ferrari has a really neat way of doing this. The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive. The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam.
THE FUTURE
If all this exotic variable valve timing technology is commonplace now, what does the future hold? Currently we are limited to either adjusting overlap by moving a standard camshaft, or switching between two fixed cam profiles. There is no reason (other then cost) why both systems could not be used in parallel on one engine, but the benefits may be limited. The true future of variable valve timing is infinite adjustability of both lift and timing.
The idea of opening and closing the valves with large electrical solenoids has been bounced around for several years. Many different manufacturers from Cummins to BMW have proposed such systems, and even made running prototypes. There are a few problems with electronically operated valves, but let's look at the advantages first. Current gasoline engines control part throttle airflow via a throttle plate, essentially lowering the air pressure in the intake manifold by choking it off with a partially closed throttle plate.
CONCLUSION
So after this seminar we come to know that VVT technology is going to become prominent in road cars as this technology is going to be researched a lot and may be in few years its cost of production can be brought down to incredible levels. We already kwon about the benefits of such a system and thereshould not be anyone who dislikes this technology, since in today’s eco-friendly world this technology brings a ray of hope for a cleaner and healthier environment. Already the automobile giants like Honda, Toyota, BMW, Mercedes-Benz, etc. are spending lots of money on research in this field. So VVT technology is bound to have a bright future in the automobile industry.
Variable Valve Timing.doc (Size: 459.5 KB / Downloads: 23)
INTRODUCTION
Engine breathing is analogous to the breathing of any living organism. At rest, the lungs take in the necessary amount of air for normal function. When running, the lungs and heart work faster to supply more oxygen to the system. Engines can't do that because their breathing apparatus (comprised intake manifolds, intake runners, valves, valve lift and throttle bores) is fixed.
There was a time when engines had to be big to be powerful. There was a time when engines could either be tuned for low-rpm torque or high-rpm power, but not both. There was a time was a time when a specific output of 100 hp per liter was the stuff of racecar fantasies. Today these limitations are all but gone. Getting 100 hp for each liter of displacement is now possible on cars that have to get good gas mileage, emit clean air, act civilized enough for your grandmother to drive them and sell for under $20,000
DEVELOPMENT OF VVT TECHNOLOGY
Honda broke the ice when the NSX debuted in 1991 as the first production car with a variable valve timing system. Honda's VTEC (which sort of stands for Variable valve Timing and lift Electronic Control) system, which has basically remained unchanged since then, is still one of the most effective systems for making ultra high specific output. Ferrari has a really neat way of doing this. The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive. The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. The shaft still spins just like a regular camshaft, but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized.
Porsche’s VARIOCAM
Porsche's VarioCam, used first on the 968 and know used without the fanfare on all (both) of their engines is as simple as it gets. With VarioCam, the crank drives the exhaust cam, and the intake cam is driven, via a short chain, by the exhaust cam. In order to advance and retard the intake cam, the chain tensioner on that short chain simply shifts up and down, moving the extra length in the chain from the tight side to the slack side. When the tight side has no extra chain (i.e. the chain is straight), the intake cam is fully advanced, as more chain is shifted to the tight side, the cam is retarded.
Ferrari’ Cam Advance Mechanism
Ferrari has a really neat way of doing this. The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive. The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam.
THE FUTURE
If all this exotic variable valve timing technology is commonplace now, what does the future hold? Currently we are limited to either adjusting overlap by moving a standard camshaft, or switching between two fixed cam profiles. There is no reason (other then cost) why both systems could not be used in parallel on one engine, but the benefits may be limited. The true future of variable valve timing is infinite adjustability of both lift and timing.
The idea of opening and closing the valves with large electrical solenoids has been bounced around for several years. Many different manufacturers from Cummins to BMW have proposed such systems, and even made running prototypes. There are a few problems with electronically operated valves, but let's look at the advantages first. Current gasoline engines control part throttle airflow via a throttle plate, essentially lowering the air pressure in the intake manifold by choking it off with a partially closed throttle plate.
CONCLUSION
So after this seminar we come to know that VVT technology is going to become prominent in road cars as this technology is going to be researched a lot and may be in few years its cost of production can be brought down to incredible levels. We already kwon about the benefits of such a system and thereshould not be anyone who dislikes this technology, since in today’s eco-friendly world this technology brings a ray of hope for a cleaner and healthier environment. Already the automobile giants like Honda, Toyota, BMW, Mercedes-Benz, etc. are spending lots of money on research in this field. So VVT technology is bound to have a bright future in the automobile industry.